YouTube's movies channel are showing blank pages with HTML5 error.
I noticed it on the previous version tonight, then updated to 2.5.1525.40 hoping that would resolve it. Not certain when this started, because I had been previously using an old version of vivaldi for a long time due to some of the old issues with printing PDF. Updated to the previous version after it was released since the PDF issue had been resolved, but hadn't gone to the free movies or movies section of YouTube since then. I turned off all of my extensions to make sure they were not interfering but the issue remains. I'm a YouTube partner creator who is on YouTube everyday and haven't noticed any other YouTube related issues until this one.
Screen Capture attached, and link to the video I was trying to reach (also tried others). https://www.youtube.com/watch?v=-IhADNJsO1Y
Screen Capture below

Enable Use of HWA in Vivaldi Settings → Webpages
and try to override GPU blacklist:

Open vivaldi://flags/#ignore-gpu-blacklist

Set To Enabled

Restart Vivaldi

Thanks @Gwen-Dragon
Tried both of those steps and neither of them resolved the issue.
Even the newest update didn't resolve the issue.
I ended up creating a test Stand Alone to see if the issue occurs in a fresh install and didn't have the Black HTML YouTube issue, Daily Motion Issue or old the .PDF issue that the update the other day resolved.
However, when I went back to my primary Stand Alone install that I've been updating for quite a while, the YouTube issue and more recent Daily Motion issue that broke with one of the previous updates still exists.
You know, it could simply be something got corrupted in the original Stand Alone install by one of the updates. Either way, I'll switch other to the fresh install, and that's what I would recommend anyone else who might come across similar issues try also. (They just want to make sure to turn on Vivaldi Sync for everything before doing the fresh install, so everything sets up easily on the new installation)
Thanks for your help as always.